Flat optical element and production method therefor

ABSTRACT

The purpose is to obtain efficiently, from a large piece of flat optical material, flat optical elements that allow for miniaturization of optical devices because they are octagonal, and that can be fixed securely in the inner opening of permanent magnets by brazing. Rounded openings  11, 12  . . . that are circular or elliptical in shape are made at intersections P 1 , P 2  . . . of the cut lines C 1 , C 2  . . . at which flat optical material  10  is cut vertically and horizontally; the flat optical material  10  in which the openings  11, 12  . . . have been made is cut vertically and horizontally; and a number of flat optical elements, each with a nearly octagonal outline with sides that are alternately four straight lines and curves, are obtained.

FIELD OF TECHNOLOGY TO WHICH INVENTION BELONGS

This invention is concerned with improvement of flat optical elementsused as Faraday rotators, polarizers and analyzers, and a productionmethod for these optical elements.

BACKGROUND OF INVENTION

Ordinarily, Faraday rotators, polarizers and analyzers are combined asflat optical elements to make up optical devices such as opticalisolators, optical regulators, wavelength division multiplexors (WDM),field sensors, optical switches and so on. To improve productivity inthe manufacture of these flat optical elements, multiple pieces areobtained by cutting a large piece of optical material that has thecharacteristics needed for each element.

The flat optical element is made from a large area of flat materialwhich is cut vertically and horizontally, under JPO Kokai PatentS64-79721 (1989), and its shape is square. These square elements do notwaste the optical material, all of which is used efficiently.

An optical device constituted by assembling these optical elements hasan effective diameter (the device aperture) for incident light andoutput light, and the flat optical element must be larger than theminimum effective diameter. Therefore, the diagonal measurement of asquare element will be 2½ times the minimum effective diameter, andbecause it is assembled within the inside diameter of a permanentmagnet, miniaturization of the optical device is blocked by thatstructure.

In making up the optical device by assembling these optical elements itis necessary to fix the optical element within the inner diameter of apermanent magnet; fixing with an adhesive or a metal fixture of Au/Snbrazing material. However, because fixing with an adhesive lacksreliability because of such things as deterioration of the adhesive, ametal fixture with brazing material is generally used.

When the four corners are fixed by brazing, the yield of the opticalmaterial is liable to drop by reason of cracks which easily form inoptical material because there is a difference in the index of thermalexpansion of the optical material and the brazing material, and a greatdifference in area of the fixed portion of one corner and that of theadjacent corner.

Aside from the square elements, there have been proposals such as JPOPatent 2838153 for polygonal flat optical elements with more than 4sides, such as hexagons or octagons. These shapes are effective forminiaturization of optical devices and for mitigation of the thermalexpansion that accompanies brazing.

However, the cutting involved in processing this flat optical materialinto hexagonal shapes is a time-consuming process, since it is necessaryto rotate the large sheet of material repeatedly from 0° to 120°.Moreover, there are more scraps of optical material, and the yield is60% that of square shapes; the lower yield means higher costs.

Production of octagonal pieces requires a two-step process, firstcutting the flat optical material into squares, and then cutting thefour corners at a slant. For that reason, the processing is moretime-consuming than when hexagonal shapes are processed, and producesmore scrap, raising the cost.

The permanent magnets into which the flat optical elements are assembledcan be formed with an inner opening that is round, or with across-sectional shape that matches the outline of the flat opticalelement. The octagonal shape has less space between the outline of theelement and the inner opening of the permanent magnet, and has theadvantage for polarizers and analyzers of a smaller region that does notoverlap the beam direction, so that the return beam is blocked fully.

Because of the lesser space between the outline of the element and theinner opening of the permanent magnet, however, the brazing accumulationof these octagonal pieces is inadequate. For this reason, there is theworry of poor fixture of flat optical elements by brazing.

The purpose of this invention is to provide flat optical devices that,because they are nearly octagonal, allow miniaturization of opticaldevices, and flat optical elements that can be fixed securely within theinner opening of the permanent magnet by brazing.

This invention also has the purpose of providing a method of productionof flat optical elements that is capable of efficiently obtainingmultiple flat optical elements from a large piece of flat opticalmaterial.

OVERVIEW OF INVENTION

The flat optical elements of this invention are formed with nearlyoctagonal outlines, with sides that are alternately four straight linesand curves.

In the method of producing flat optical elements of this invention,multiple flat optical elements are obtained by making openings that arecircular or elliptical in shape at intersections of the cut lines atwhich the flat optical material is cut vertically and horizontally,cutting the flat optical material in which the openings have been madevertically and horizontally, and obtaining a number of flat opticalelements, each with a nearly octagonal outline with sides that arealternately four straight lines and curves.

BRIEF EXPLANATION OF DRAWINGS

FIG. 1 is a plane view of a flat optical element of one example of thisinvention.

FIG. 2 is a plane view of a flat optical element of another example ofthis invention.

FIG. 3 is an explanatory drawing showing the method of producing theflat optical elements of this invention.

FIG. 4 is a plane view of one example of an opening made in the methodof producing flat optical elements of this invention.

FIG. 5 is a plane view of another example of a rounded opening made inthe method of producing flat optical elements of this invention.

FIG. 6 is an explanatory drawing showing one example of assembling theflat optical element of this invention in a permanent magnet.

FIG. 7 is an explanatory drawing showing another example of assemblingthe flat optical element of this invention in a permanent magnet.

OPTIMUM MODE OF IMPLEMENTATION

To explain with reference to the attached drawings, FIGS. 1 and 2 showthe optimum shape for constitution of a flat optical element 1 asFaraday rotator, a polarizer or an analyzer. This shape has an outlinethat is nearly octagonal, with four straight sides 1 a to 1 dalternating with four curved sides 1 e to 1 h.

Of these, Faraday Rotators would use as the optical material a sheet ofa material such as Faraday glass, magnetic garnet crystal or Cd—Mn—Te—Hgcrystal. In the case of polarizers or analyzers, a material which isformed by vapor deposition such as a polarized beam splitter on a basematerial as birefringent material like polarized glass orrutile-calcite-lithium niobate, would be used as a flat opticalmaterial.

To manufacture these flat optical elements, openings 11, 12 . . . thatare rounded in shape are made at intersections P1, P2 . . . of the cutlines C1, C2 . . . at which the flat optical material 10 is cutvertically and horizontally as shown in FIG. 3; the flat opticalmaterial 10 in which the openings 11, 12 . . . have been made is cutvertically and horizontally; and a number of flat optical elements, eachwith a nearly octagonal outline in which straight sides 1 a to 1 dalternate with curved sides 1 e to 1 h, are obtained.

The means of cutting the rounded openings 11, 12 . . . (only 11 islabeled in the drawings) can be a diamond drill, laser, ultrasonicwaves, etching, or other means as appropriate. The shape of the openingscan be either elliptical, as shown in FIG. 4, or circular as shown inFIG. 5. By forming the openings 11, 12 . . . and cutting the surface ofthe optical material 10 vertically and horizontally, each quarter of arounded opening 11, 12 . . . corresponds to one curved side 1 e to 1 h.

These curved sides 1 e to 1 h are connected at intervals averaging 45°,alternating with straight sides 1 a to 1 d through 360° as shown in FIG.1. It is possible, as shown in FIG. 2, to instead have curves 1 e to 1 hwith a smaller radius of curvature, in which their length is equal to orless than that of the straight sides 1 a to 1 d.

The octagonal shape shown in FIG. 2 is taken as a specific examplebecause of its overall balance. Using garnet single crystal as the basematerial for Faraday rotators, or polarized glass as the base materialfor polarizers or analyzers, a diamond drill with a drill diameter of0.8 mm was used to make circular openings at intervals of 2 mmvertically and horizontally. Because of the 2 mm vertical and horizontalspacing, it was possible to obtain Faraday rotators, polarizers oranalyzers measuring 2 mm vertically and horizontally with the corners R0.8 mm, effective diameter Φ 1.7 mm.

In addition, using garnet single crystal as the base material forFaraday rotators, or glass substrate formed with a polarized beamsplitter by vapor deposition as the base material for polarizers oranalyzers, a laser with a laser diameter of 0.6 mm was used to makecircular openings at intervals of 1.5 mm vertically and horizontally.Because of the 1.5 mm vertical and horizontal spacing, it was possibleto obtain Faraday rotators, polarizers or analyzers measuring 1.5 mmvertically and horizontally with the corners R 0.6 mm, effectivediameter Φ 1.3 mm.

When nearly octagonal flat optical elements are produced in this way, itis possible not only to build smaller optical devices because of theoctagonal shape, but also to obtain multiple flat optical elements atone time by cutting multiple openings in a large sheet of opticalmaterial, and making vertical and horizontal cuts. Consideredcomprehensively, therefore, it is possible to reduce costs and obtainflat optical elements with which optical devices can be builtinexpensively.

When these flat optical elements 1 are fixed inside permanent magnets 2,whether the inside shape of the permanent magnet is rounded as shown inFIG. 6 or octagonal as shown in FIG. 7, there are relatively large gapsbetween the inside shape of the permanent magnet 2 and the curved sides1 e to 1 h of the nearly octagonal flat optical element 1.

Because it is possible to use these gaps to accommodate brazingmaterial, it is possible to fix the flat optical element 1 firmly withinthe inside shape of the permanent magnet 2.

The brazing strength for octagonal pieces is about 1600 g/mm² for theusual bottom surface brazing, but under this invention it can be over2200 g/mm², because side surface brazing occurs as well.

INDUSTRIAL UTILITY

As stated above, using the flat optical elements of this invention, itis possible to build highly reliable optical devices in which the flatoptical elements are fixed firmly within the inner shape of thepermanent magnet, since the outline of the flat optical element isnearly octagonal, with alternating straight sides and curved sides, suchthat there are relatively large gaps that can accommodate brazingmaterial between the curved sides of the nearly octagonal shape and theinner shape of the permanent magnet.

Using the method of producing flat optical elements of this invention,openings that are circular or elliptical in shape are made atintersections of the cut lines at which the flat optical material is cutvertically and horizontally, the flat optical material in which theopenings have been made is cut vertically and horizontally, and a numberof flat optical elements, each with a nearly octagonal outline withsides that are alternately four straight lines and curves, are obtained,so that it is possible not only to use the flat optical elements inoptical devices that are smaller, but also to obtain multiple flatoptical elements at one time by cutting multiple openings in a largesheet of optical material, and making vertical and horizontal cuts,making it possible to reduce costs and build optical devicesinexpensively.

The terms and expressions used in the description of the invention aboveare used simply for the purpose of explanation, and in no way limit thecontent of this invention. The use of any limiting terms or expressionsis not intended to exclude an modality that is equivalent to theinvention as described above, or any portion thereof. It is clear,therefore, that it is possible to make various changes within the scopeof this invention for which rights are claimed.

What is claimed is:
 1. Flat optical elements used as Faraday rotators,polarizers or analyzers, in which each optical element has a nearlyoctagonal outline with sides that are alternately four straight linesand curves, wherein the radius of curvature of each curve issubstantially equal to the length of each straight line.
 2. A method ofproducing flat optical elements that are suited to obtaining, from alarge piece of flat optical material, multiple flat elements that arenearly octagonal and can be used as Faraday rotators, polarizers oranalyzers; in which openings that are circular or elliptical in shapeare made at intersections of cut lines at which the flat opticalmaterial is cut vertically and horizontally; the flat optical materialin which the openings have been made is cut vertically and horizontally;and a number of flat optical elements, each with a nearly octagonaloutline with sides that are alternately four straight lines and curves,are obtained.
 3. A method of producing multiple flat optical elements,comprising: providing a single piece of flat optical material; makingopenings in the single piece of flat optical material, located atintersections of vertical and horizontal cut lines; and cutting, alongthe horizontal and vertical cut lines to obtain multiple flat opticalelements that are shaped substantially octagonal.
 4. The method of claim3, wherein the openings are circular or elliptical.
 5. The method ofclaim 3, wherein the radius of curvature of each curve is substantiallyequal to the length of each straight line.